2006 mercury 15hp compression question

G

Guest

Guest
Hi all, when I check compression I get 90 on top and about 80 at bottom but for the bottom cylinder I have pull like 12-15 times and break a sweat. Is that's normal? When I see people do it on YouTube they do it in 3-4 pulls with ease??? I also noticed the string got really tight to pull and once I pulled it out the compression went up?? What can that be is the engine bad?
 
Last edited:
O

oldman570

Lieutenant Commander
Joined
Mar 25, 2011
Messages
1,615
Re: 2006 mercury 15hp compression question

The compression test should be done with both plugs out of the motor and the plug wires grounded out to the block. The prop removed and the throttle in the FWD wide open position so the cylinder's get plenty of air to compress. The pull rope should be very easy to pull when done this way. If the readings are more than 10% difference then the motor should be looked into for damage to the pistons, rings, and cylinder walls. If damage is indicated, then pulling the intake and/or exhaust port plates will let you look for damage to those parts. JMO
Oldman570
 
R

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,269
Re: 2006 mercury 15hp compression question

Throttle does not need to be open on a 2 stroke motor.---------Exhaust ports are wide open and compression does not start untill after the piston closes them off.
 
G

Guest

Guest
Re: 2006 mercury 15hp compression question

racerone said:
Throttle does not need to be open on a 2 stroke motor.---------Exhaust ports are wide open and compression does not start untill after the piston closes them off.
Click to expand...

Thanks for everyones help!!! Its a 4 stroke. As soon as i get back from work tonight i will try try with both plugs removed in full throttle and it fwd gear. I tried again last night in nuetral with both plugs removed ans got like 110 in top and like 50 on the bottom.( weird part was that i kept pulling the rope while connected to bottom cyl and took a whilw but it got up to 80. Still a big difference) I havent tried in fwd with throttle open. Hope i have better results
 
R

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,269
Re: 2006 mercury 15hp compression question

I missed the 4 stroke part.
 
You must log in or register to reply here.
Top